CN114907605A

CN114907605A - Edible nano composite film and preparation method and application thereof

Info

Publication number: CN114907605A
Application number: CN202210697328.8A
Authority: CN
Inventors: 王劲松; 李�瑞
Original assignee: Jingchu University of Technology
Current assignee: Jingchu University of Technology
Priority date: 2022-06-20
Filing date: 2022-06-20
Publication date: 2022-08-16
Anticipated expiration: 2042-06-20
Also published as: CN114907605B

Abstract

The invention discloses an edible nano composite film and a preparation method and application thereof, wherein the edible nano composite film comprises the following components in parts by weight: 0.1-0.2 part of hydrophilic nano phytoglycogen, 0.1-0.5 part of oregano essential oil, 1-2 parts of sodium alginate, 1-2 parts of tween 80, 1-2 parts of glycerol and 0.01-0.02 part of calcium chloride, and the preparation method comprises the following steps: s1, dispersing sodium alginate, glycerol and Tween 80 into a hydrophilic nano phytoglycogen aqueous solution, and dropwise adding oregano essential oil under the condition of heating and stirring to obtain a mixed solution; s2, dropwise adding a calcium chloride solution into the mixed solution under a heating and stirring state to obtain a membrane solution; s3, casting the membrane liquid into a membrane, and drying at room temperature to obtain a crude product of the composite membrane; s4, soaking the crude product of the composite film in a calcium chloride solution of glycerol, then soaking the crude product of the composite film in an aqueous solution of the glycerol, then washing the crude product of the composite film with the aqueous solution of the glycerol, and standing the crude product of the composite film in an environment with the water content of 50-55% at the temperature of 20-25 ℃ to obtain the edible nano composite film, wherein the edible nano composite film has good mechanical property and fresh-keeping effect.

Description

Edible nano composite film and preparation method and application thereof

Technical Field

The invention relates to the technical field of food packaging, in particular to an edible nano composite film and a preparation method and application thereof.

Background

The quality safety of food has been the focus of food packaging research, and food packaging is mainly used for preserving food raw materials, prolonging the shelf life of food, maintaining the quality of food, delaying deterioration, preventing the negative effects of transportation and the like, and a food packaging system must be capable of protecting food from factors such as heat, oxygen, moisture, enzymes, microorganisms, unpleasant odor components and the like, and preventing the loss of aroma, particularly for fresh fruits, vegetables and the like, the marketability of the food is mainly determined by appearance, flavor, color, texture, nutritional value and microbial safety, and the food packaging material is more challenging.

Fresh cut fruits and vegetables provide a convenient food form for consumers while still maintaining fresh quality. The shelf life of fresh-cut fruits or vegetables is significantly shorter than their intact form, and the overall quality and shelf life of fresh-cut fruits and vegetables is reduced by factors such as water loss, enzymatic browning, texture deterioration, ripening processes and microbial growth. These putrefaction processes are accelerated by tissue damage caused by peeling, slicing and cutting. At present, the fresh-keeping mode for fresh-cut fruits and vegetables is coating fresh-keeping, and the coating fresh-keeping adopts the mode that a layer of protective film is formed on the surface of the whole fruit or the surface of the fresh-cut fruit, so that on one hand, the respiration of the fruit can be blocked, on the other hand, the water loss of the fruit can be avoided, the invasion of microorganisms can be isolated to a certain degree, and the fresh-keeping mode is the most suitable fresh-keeping mode for the fresh-cut fruits at present. However, the optimal preservation time of film fresh-cut fruits is short, and the fruits are subjected to anaerobic respiration due to respiration inhibition, so that the fruits are subjected to uncomfortable senses similar to fermentation, and the taste of the fruits is not easy to be accepted by consumers.

Compared with the film-coating preservation mode, the semi-permeable barrier provided by the edible preservative film is used for prolonging the shelf life by reducing the migration of moisture and solute, gas exchange, respiration and oxidation reaction rates, inhibiting the physiological maturation process of fresh-cut fruits, prolonging the shelf life of the fresh-cut fruits and vegetables, and preventing insect pests, microorganism propagation and pollution caused by other types of decay, for example, Chinese patent with publication number CN110250262A discloses an edible fresh-cut fruit preservative film and a preservation method, which can maintain the respiration of fruits for a longer time and prolong the preservation time, but have poorer mechanical properties for taking account of air permeability.

Disclosure of Invention

In view of the above, the present application provides an edible nanocomposite film, and a preparation method and an application thereof, which have good mechanical properties and a good fresh-keeping effect.

In order to achieve the technical purpose, the following technical scheme is adopted in the application:

in a first aspect, the present application provides an edible nanocomposite film, comprising the following components in parts by weight: 0.1-0.2 part of hydrophilic nano phytoglycogen, 0.1-0.5 part of oregano essential oil, 1-2 parts of sodium alginate, 1-2 parts of tween 80, 1-2 parts of glycerol and 0.01-0.02 part of calcium chloride.

Preferably, the edible nano composite film comprises the following components in parts by weight: 0.1 part of hydrophilic nano phytoglycogen, 0.1 part of oregano essential oil, 1 part of sodium alginate, 1 part of

tween

80, 1 part of glycerol and 0.01 part of calcium chloride.

In a second aspect, the present application provides a method of preparing an edible nanocomposite film, comprising the steps of:

s1, dispersing sodium alginate, glycerol and Tween 80 into a hydrophilic nano phytoglycogen water solution, and dropwise adding oregano essential oil under the heating and stirring state to obtain a mixed solution;

s2, dropwise adding a calcium chloride solution into the mixed solution under a heating and stirring state to obtain a membrane solution;

s3, carrying out tape casting on the membrane liquid to form a membrane, and drying at room temperature to obtain a crude product of the composite membrane;

s4, soaking the crude product of the composite film in a calcium chloride solution of glycerol, then soaking the crude product of the composite film in an aqueous solution of the glycerol, then washing the crude product of the composite film with the aqueous solution of the glycerol, and then standing the crude product of the composite film in an environment with the temperature of 20-25 ℃ and the moisture content of 50-55% to obtain the edible nano composite film.

Preferably, in the step S1 and the step S2, the heating and stirring temperature is 60-70 ℃, and the stirring speed is 80-100 rpm.

Preferably, the method also comprises the step of carrying out suction filtration on the aqueous solution of the hydrophilic nano phytoglycogen to remove impurities.

Preferably, the preparation method of the hydrophilic nano phytoglycogen comprises the following steps:

K1. dispersing and soaking the crushed sweet corns in deionized water, and filtering to remove filter residues to obtain a first supernatant;

K2. adjusting the pH value of the first supernatant to be acidic, and then performing centrifugal separation to obtain a second supernatant;

K3. adjusting the pH value of the second supernatant to be neutral, boiling, cooling and centrifugally separating to obtain a polysaccharide solution;

K4. adding absolute ethyl alcohol into the polysaccharide solution, standing overnight at 4 ℃, performing suction filtration, drying a filter cake obtained by suction filtration, and grinding to obtain the hydrophilic nano phytoglycogen.

Preferably, in step K2, the pH is 4.5 to 4.9.

Preferably, the preparation method of the oregano essential oil comprises the following steps: and (3) soaking the dried oregano in absolute ethyl alcohol at room temperature, carrying out suction filtration, and carrying out rotary evaporation drying on an extracting solution obtained by suction filtration under a vacuum condition to obtain the oregano essential oil.

In a third aspect, the application provides an application of the edible nano composite film as a preservative film in fruit and vegetable preservation.

Preferably, the fruits and vegetables are fresh-cut fruits and vegetables.

The beneficial effect of this application is as follows:

1. the composite membrane has the advantages that sodium alginate is used as a membrane forming substrate, a membrane forming formula is optimized, oregano essential oil and hydrophilic nano phytoglycogen are used for modifying the membrane to form a three-dimensional network structure, the obtained composite membrane is good in mechanical property and membrane forming property, strong in antibacterial and antioxidant performance and low in water vapor transmission rate, the micro-air-conditioned environment on the surface of the fruits and vegetables can be maintained, and the shelf life of the fresh-cut fruits and vegetables is effectively prolonged;

2. by adding the Tween 80 and the glycerol, the rigid structure of the composite film is softened, the flexibility of the composite film is increased, the barrier property is reduced, and the composite film is glossy and elastic;

3. the composite film of the scheme is degradable, has no toxic or side effect and is environment-friendly.

Drawings

FIG. 1 is a transmission electron microscope image of water-soluble nano phytoglycogen;

FIG. 2 shows the change of the composite film coating of "Red Fuji" fresh-cut apples stored for 4 days;

FIG. 3 shows the effect of origanum essential oil/phytoglycogen/sodium alginate composite membrane treatment on the weight loss rate of fresh-cut red Fuji apples;

FIG. 4 shows the effect of origanum essential oil/phytoglycogen/sodium alginate composite membrane treatment on color difference of fresh-cut red Fuji apples;

FIG. 5 is a graph of the effect of oregano essential oil/phytoglycogen/sodium alginate composite membrane treatment on the hardness of fresh-cut "Red Fuji" apples;

FIG. 6 shows the effect of oregano essential oil/phytoglycogen/sodium alginate composite membrane treatment on the soluble solids content of fresh-cut "Red Fuji" apples;

FIG. 7 is a graph showing the effect of oregano essential oil/phytoglycogen/sodium alginate composite membrane treatment on the total acidity of freshly cut "Hongfush" apples;

FIG. 8 is a graph of the effect of oregano essential oil/phytoglycogen/sodium alginate composite membrane treatment on ascorbic acid in freshly cut "Red Fuji" apples;

FIG. 9 is a graph showing the effect of origanum essential oil/phytoglycogen/sodium alginate composite membrane treatment on the total number of colonies of freshly cut "Red Fuji" apples;

FIG. 10 shows basic parameters of each composite film;

FIG. 11 shows the functional parameters of each composite membrane.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Natural polysaccharides are of increasing interest to researchers as food packaging materials because they are abundant, sustainable, environmentally friendly, low-toxic, biodegradable and biocompatible. Among various polysaccharides, sodium alginate extracted from brown seaweed shows great potential as a film forming material due to its excellent film forming property, non-toxicity and unique colloidal characteristics, and a film obtained from alginate is uniform and transparent and has good oxygen barrier property. However, sodium alginate-based films exhibit poor moisture resistance due to their high hydrophilicity, which may limit their use in food packaging applications, and in order to improve their performance, modification or blending methods are employed, which can effectively promote the intermolecular crosslinking of sodium alginate and modify the polymer network to achieve the goal of improving the film performance, which provides a concept for preparing edible composite films.

However, sodium alginate is used as a film forming substrate to modify and prepare the edible composite film, in order to maintain the micro-air-conditioning environment on the surface of the fruits and vegetables, the edible composite film needs to have certain air permeability, and the improvement of the air permeability often brings about the reduction of the mechanical performance, so that the two are difficult to be considered, and the defects which are difficult to overcome by the technical personnel in the field are overcome.

The essential oil of oregano mainly comprises carvacrol (with the content of 80-85%), thymol (with the content of 2.5-3%), p-cymene (with the content of 3.5-9%) and gamma-terpinene (with the content of 2.0-5.5%), and is a natural antibacterial agent, strong antibacterial activity is mainly derived from the thymol and the carvacrol, and the essential oil has excellent antibacterial capability on escherichia coli, staphylococcus aureus, salmonella, candida albicans, staphylococcus epidermidis, klebsiella pneumoniae and enterobacter aerogenes, in particular to pseudomonas aeruginosa, proteus mirabilis, escherichia coli 25922 and pseudomonas aeruginosa 10145; meanwhile, the oregano essential oil has strong antioxidant activity, and the effective components playing the antioxidant effect mainly comprise phenolic acids and terpene compounds, and the oregano essential oil is usually used as a preservative by the prior art;

phytoglycogen is a highly branched water-soluble glucan found in plants, and is composed of glucose units connected by alpha-1, 4 and alpha-1, 6 glycosidic bonds, the average chain length DP is 10-12, the particle size is 30-100 nm, the phytoglycogen dispersed in an aqueous solution is uniform spherical nanoparticles, the branch density and the molecular density are respectively 7-10%, and 1000-2000g/mol nm ³ The dendritic structure of PG has many characteristics that are clearly distinguished from similar molecular weight plant polysaccharides, such as high water retention, low viscosity, high stability and monodispersity.

The applicant unexpectedly finds that in the process of improving the sodium alginate polymer network, the composite film prepared by using the hydrophilic nano phytoglycogen, the origanum oil and the sodium alginate as raw materials can form a hydrogen bond through the interaction of the hyperbranched structure of the hydrophilic nano phytoglycogen, the sodium alginate and the origanum oil, so that a three-dimensional network is formed, the structure is stable, the toughness of the composite film is improved while the quality effect of fruits and vegetables is maintained through the synergistic effect, the mechanical property is improved, and the film forming property is improved.

The embodiment of the application provides an edible nano composite film, which comprises the following components in parts by weight: 0.1-0.2 part of hydrophilic nano phytoglycogen, 0.1-0.5 part of oregano essential oil, 1-2 parts of sodium alginate, 1-2 parts of tween 80, 1-2 parts of glycerol, 0.01-0.02 part of calcium chloride and the balance of deionized water, wherein the mass ratio of the hydrophilic nano phytoglycogen to the oregano essential oil to the sodium alginate is 1-2:1-5:10-20, preferably, the mass ratio of the hydrophilic nano phytoglycogen to the oregano essential oil to the sodium alginate is 1: 1-5: 10.

in some embodiments, the edible nanocomposite film comprises the following components in parts by weight: 0.1 part of hydrophilic nano phytoglycogen, 0.1 part of oregano essential oil, 1 part of sodium alginate, 1 part of

tween

80, 1 part of glycerol, 0.01 part of calcium chloride and the balance of deionized water.

In the scheme, the hydrophilic nano phytoglycogen has high water retention, low viscosity, high stability and high water solubility, and the super branched chain structure of the hydrophilic nano phytoglycogen can form an intermolecular hydrogen bond action with sodium alginate and oregano essential oil to form a three-dimensional network structure; meanwhile, the nano phytoglycogen and the oregano oil can form a synergistic antibacterial effect, and the oregano oil can enable the composite membrane to have an antioxidant function; the sodium alginate has good film forming property, degradability and edibility, interacts with the oregano oil and the nano-phytoglycogen to enhance the film forming property of the composite film, and the three cooperate to obtain the edible composite film with good mechanical property and fresh-keeping effect; in addition, the addition of tween 80 and glycerin softens the rigid structure of the film, thereby increasing the flexibility of the film, reducing the barrier property of the film, and making the film glossy and elastic.

Embodiments of the present application also provide a method for preparing an edible nanocomposite film, comprising the steps of:

s1, weighing 0.1-0.2 part of hydrophilic nano phytoglycogen, 0.1-0.5 part of oregano essential oil, 1-2 parts of sodium alginate, 1-2 parts of tween 80, 1-2 parts of glycerol and 0.01-0.02 part of calcium chloride according to parts by mass, dispersing the hydrophilic nano phytoglycogen into deionized water to prepare a 0.1-0.2 wt% hydrophilic nano phytoglycogen aqueous solution, stirring, carrying out suction filtration to remove insoluble impurities, adding the sodium alginate, the glycerol and the tween 80 into the hydrophilic nano phytoglycogen aqueous solution, stirring for 3 hours at the temperature of 60-70 ℃ and at the stirring speed of 80-100rpm, and dropwise adding the oregano essential oil in the stirring process to obtain a mixed solution, wherein the concentration of the oregano essential oil in the mixed solution is 0.1-0.5 wt%;

s2, magnetically stirring for 4 hours at the temperature of 60-70 ℃ and at the stirring speed of 80-100rpm, and dropwise adding a calcium chloride aqueous solution into the mixed solution to obtain a membrane solution, wherein the final concentration of calcium chloride in the obtained membrane solution is 0.01-0.02 wt%;

s3, naturally casting the membrane liquid on an acrylic plate to form a membrane, and drying at room temperature for 24h +/-2 h to obtain a crude product of the composite membrane;

s4, soaking the crude product of the composite film in a calcium chloride solution of glycerol, then soaking the crude product of the composite film in an aqueous solution of the glycerol, then washing the crude product of the composite film with the aqueous solution of the glycerol for two to three times, and standing the crude product of the composite film for 2 days at the temperature of 20-25 ℃ in an environment with the water content of 50-55%, thus obtaining the edible nano composite film.

The preparation method of the hydrophilic nano phytoglycogen comprises the following steps:

K1. crushing commercial sweet corn kernels by using a universal crusher, adding the crushed commercial sweet corn kernels into deionized water with the weight 5 times that of the commercial sweet corn kernels, continuously stirring the mixture during the stirring, finely polishing the mixture for 24 hours at the temperature of 4 ℃, and filtering the mixture by using 8 layers of gauze to remove filter residues to obtain a first supernatant;

K2. adjusting the pH value of the first supernatant to 4.5-4.9 with 0.1mmol/L hydrochloric acid, standing for a period of time, centrifuging at 8000rpm for 10min, and removing protein precipitate to obtain a second supernatant;

K3. adjusting the pH value of the second supernatant to 7.0 by using 0.1mmol/L sodium hydroxide solution, boiling and keeping for 30min, cooling, and centrifuging at 8000rpm for 10min to obtain polysaccharide solution;

K4. adding 3 times volume of absolute ethyl alcohol into the polysaccharide solution, stirring while adding, standing in a refrigerator at 4 ℃ overnight, performing suction filtration, repeatedly washing a filter cake obtained by suction filtration with absolute ethyl alcohol for 2-3 times, drying at 60 ℃, grinding into powder, and sieving by a 80-mesh sieve to obtain the hydrophilic nano phytoglycogen.

The preparation method of the oregano essential oil comprises the following steps: soaking 100g of dried oregano in absolute ethyl alcohol for 3 days at room temperature, wherein the extraction is not applicable, directly performing suction filtration, drying an extracting solution obtained by suction filtration in a rotary evaporator for 24 hours under a vacuum condition (40 ℃, 178mbar) to obtain the oregano essential oil, and performing gas chromatography-mass spectrometry to obtain the oregano essential oil with the concentration of 896.6 mg/mL.

The embodiment of the application also provides application of the edible nano composite film as a preservative film in fruit and vegetable preservation, in particular to the preservative film for fresh-cut fruits and vegetables.

Raw material preparation

Preparation of hydrophilic nano-phytoglycogen: K1. crushing fresh and sweet corn kernels with Su-1 genotypes by a universal crusher, adding the crushed fresh and sweet corn kernels into deionized water with the weight 5 times that of the crushed fresh and sweet corn kernels, continuously stirring the mixture during the process, finely polishing the mixture at the temperature of 4 ℃ for 24 hours, and filtering the mixture by using 8 layers of gauze to remove filter residues to obtain first supernatant; K2. adjusting the pH value of the first supernatant to 4.5-4.9 by using 0.1mmol/L hydrochloric acid, standing for a period of time, centrifuging at 8000rpm for 10min, and removing protein precipitate to obtain a second supernatant; K3. adjusting the pH value of the second supernatant to 7.0 by using 0.1mmol/L sodium hydroxide solution, boiling and keeping for 30min, cooling, and centrifuging at 8000rpm for 10min to obtain polysaccharide solution; K4. adding 3 times volume of absolute ethyl alcohol into the polysaccharide solution, stirring while adding, standing in a refrigerator at 4 ℃ overnight, performing suction filtration, repeatedly washing a filter cake obtained by suction filtration with absolute ethyl alcohol for 2-3 times, drying at 60 ℃, grinding into powder, and sieving by a 80-mesh sieve to obtain the hydrophilic nano phytoglycogen.

Preparing oregano essential oil: soaking 100g of dried oregano in absolute ethyl alcohol for 3 days at room temperature, wherein the extraction is not applicable, directly performing suction filtration, drying an extracting solution obtained by suction filtration in a rotary evaporator for 24 hours under a vacuum condition (40 ℃, 178mbar) to obtain the oregano essential oil, and performing gas chromatography-mass spectrometry to obtain the oregano essential oil with the concentration of 896.6 mg/mL.

Example 1

A preparation method of an edible nano composite film comprises the following steps:

s1, weighing 0.1 part of hydrophilic nano phytoglycogen, 0.1 part of oregano essential oil, 1 part of sodium alginate, 1 part of

tween

80, 1 part of glycerol and 0.01 part of calcium chloride according to parts by mass, dispersing the hydrophilic nano phytoglycogen into deionized water to prepare a 0.1 wt% aqueous solution of hydrophilic nano phytoglycogen, performing suction filtration after stirring to remove insoluble impurities, then adding the sodium alginate, the glycerol and the tween 80 into the aqueous solution of hydrophilic nano phytoglycogen, stirring for 3 hours at the temperature of 60 ℃ and the stirring speed of 80rpm, and dropwise adding the oregano essential oil during stirring to obtain a mixed solution, wherein the concentration of the oregano essential oil in the mixed solution is 0.1 wt%;

s2, magnetically stirring for 4 hours at the temperature of 60 ℃ and at the stirring speed of 80-100rpm, and dropwise adding a calcium chloride aqueous solution with the concentration of 0.2% (m/v) into the mixed solution to obtain a membrane solution, wherein the final concentration of calcium chloride in the obtained membrane solution is 0.01 wt%;

s4, soaking the crude product of the composite film in a calcium chloride solution (2.0 percent, m/v) containing 2 percent of glycerol (v/v), soaking in a water solution of 5 percent of glycerol (v/v) for 15min, then washing with the water solution of 5 percent of glycerol (v/v) for two to three times, and standing for 2 days at 25 ℃ in an environment with 50 percent of water content to obtain the edible nano composite film.

Example 2

s1, weighing 0.2 part of hydrophilic nano phytoglycogen, 0.5 part of oregano essential oil, 2 parts of sodium alginate, 2 parts of

Tween

80, 2 parts of glycerol and 0.02 part of calcium chloride according to parts by mass, dispersing the hydrophilic nano phytoglycogen into deionized water to prepare a 0.2 wt% aqueous solution of hydrophilic nano phytoglycogen, performing suction filtration after stirring to remove insoluble impurities, then adding the sodium alginate, the glycerol and the Tween 80 into the aqueous solution of hydrophilic nano phytoglycogen, stirring for 3 hours at 70 ℃ and a stirring speed of 100rpm, and dropwise adding the oregano essential oil during stirring to obtain a mixed solution, wherein the concentration of the oregano essential oil in the mixed solution is 0.5 wt%;

s2, magnetically stirring for 4 hours at 70 ℃ and at a stirring speed of 100rpm, and dropwise adding a calcium chloride aqueous solution with the concentration of 0.2% (m/v) into the mixed solution to obtain a membrane solution, wherein the final concentration of calcium chloride in the obtained membrane solution is 0.02 wt%;

s4, soaking the crude product of the composite film in a calcium chloride solution (2.0 percent, m/v) containing 2 percent of glycerol (v/v), soaking in a water solution of 5 percent of glycerol (v/v) for 15min, then washing with the water solution of 5 percent of glycerol (v/v) for two to three times, and standing for 2 days at the temperature of 20 ℃ in an environment with the moisture content of 55 percent to obtain the edible nano composite film.

Example 3

s1, weighing 0.1 part of hydrophilic nano phytoglycogen, 0.2 part of oregano essential oil, 1 part of sodium alginate, 1 part of

tween

80, 1 part of glycerol and 0.01 part of calcium chloride according to parts by mass, dispersing the hydrophilic nano phytoglycogen into deionized water to prepare a 0.1 wt% aqueous solution of hydrophilic nano phytoglycogen, performing suction filtration after stirring to remove insoluble impurities, then adding the sodium alginate, the glycerol and the tween 80 into the aqueous solution of hydrophilic nano phytoglycogen, stirring for 3 hours at 65 ℃ and a stirring speed of 90rpm, and dropwise adding the oregano essential oil during stirring to obtain a mixed solution, wherein the concentration of the oregano essential oil in the mixed solution is 0.2 wt%;

s2, magnetically stirring for 4 hours at 65 ℃ and at a stirring speed of 90rpm, and dropwise adding a calcium chloride aqueous solution with the concentration of 0.2% (m/v) into the mixed solution to obtain a membrane solution, wherein the final concentration of calcium chloride in the obtained membrane solution is 0.01 wt%;

s4, soaking the crude product of the composite film in a calcium chloride solution (2.0 percent, m/v) containing 2 percent of glycerol (v/v), then soaking in a water solution of 5 percent of glycerol (v/v) for 15min, then washing with the water solution of 5 percent of glycerol (v/v) for two to three times, and standing for 2 days at 23 ℃ in an environment with 52 percent of water content to obtain the edible nano composite film.

Comparative example 1

The other steps were the same as example 1, except that in step S1, hydrophilic nano phytoglycogen and oregano essential oil were not added, and an SA film was obtained.

Comparative example 2

The other steps were the same as in example 1, except that in step S1, hydrophilic nano phytoglycogen was not added, and an OEO/SA film was obtained.

Comparative example 3

The other steps were the same as in example 1, except that no oregano essential oil was added in step S1, to obtain a PG/SA film.

Test example

The films obtained in examples 1-2 and comparative examples 1-3 were tested for their properties, and the specific items and procedures were as follows:

and (3) thickness measurement: measuring the thickness of the film by using a thickness gauge with the precision of 0.001mm, measuring six points, and calculating the average value of the six points to obtain the thickness of the composite film;

and (3) measuring color difference: measuring the chromatic aberration by using a chromatic aberration meter CR-400, and taking a correction plate as a contrast to measure the total chromatic aberration value of the composite film as delta E;

and (3) measuring mechanical properties: selecting an edible composite film with a uniform surface and no cracks, taking GB/T1040.3-2006 'determination of plastic tensile property' as a standard, determining according to American Society for Testing and Materials (ASTM) standard method (2021), cutting the composite film into strips of 2cm multiplied by 10cm, and clamping the composite film on a tensile probe of a texture analyzer with two flat ends. Setting the initial distance to be 50mm, setting the stretching speed to be 0.1cm/s, making 5 groups of composite films in parallel for each group, recording the stretching length and the tension when the composite films break, and calculating the tensile strength and the elongation at break according to a formula.

Tensile Strength (TS) is the ratio of the maximum Tensile force which a membrane can bear before breaking to the cross-sectional area of the membrane under the action of Tensile force, and the unit is N/mm ³ (MPa)。

In the formula: TS is tensile strength, and the unit is MPa; f is the maximum tensile force at film break in units of N; l is the average thickness of the film in mm; w is the width of the film sample in mm.

Elongation at Break (EB) is an index reflecting the film stretching ability, and refers to the ability of a film to stretch until breaking when stretched by an external force.

In the formula: EB is elongation at break in%; l is ₀ Is the length of the film before stretching, in mm; l is a radical of an alcohol ₁ The length of the film after stretching is in mm.

And (3) water solubility determination: cutting the composite membrane into a plurality of squares with the size of 2cm multiplied by 2cm, selecting three squares, weighing the squares to obtain the weight of S, drying the squares at 105 ℃ for 4 hours, and weighing the squares to determine the weight of S ₀ . And then placing the three small square films into 100mL beakers containing 30mL of distilled water, sealing the beakers with tinfoil, and placing the beakers under the conditions of 25 ℃ and 120rpm/min and shaking for 24 hours at constant temperature. The undissolved film is then removed, rinsed 2 times with distilled water, dried at 105 ℃ for 4h and weighed as S ₁ To determine the dissolution mass. The Water solubility of the film (Water solution, WS) is calculated as follows:

in the formula: WS is membrane water soluble in units; s ₀ Is the initial dry matter in g; s ₁ Is undissolved dry matter and is given in g.

And (3) water content determination: composite membrane weighing m ₀ Drying at 105 deg.C for 4h, weighing the composite membrane ₁ And calculating to obtain the water content. The water Content (MC) of the film is calculated as follows:

in the formula: MC is water content, unit is%; s is the initial weight of the composite membrane, and the unit is g; s. the ₀ Is the initial dry matter in g.

And (3) swelling degree determination: cutting the composite membrane into squares with the size of 2cm multiplied by 2cm, weighing, immersing in a beaker containing 30mL of distilled water, taking out once every 30min at room temperature, quickly absorbing the surface water of the composite membrane by using filter paper after taking out, and weighing until the weight difference of the front and the back is less than 0.01 g. And (5) accurately calculating to obtain the swelling degree of the composite membrane.

In the formula: SD is the degree of membrane swelling, in units; m is ₁ Mass of membrane after swelling, unit is g; m is ₀ The mass of the membrane before swelling is given in g.

And (3) measuring the water vapor transmission rate: and 3.0g of dried anhydrous calcium chloride is filled in the dried drying dish, vaseline is coated on the edge of the opening of the drying dish in a circle, the opening is sealed by a film sample, and the whole process is operated under an infrared lamp, so that the exposure time in the air is reduced. These dishes were each stored in a vacuum desiccator containing a saturated sodium chloride solution to obtain a relative humidity of 75. + -. 2%. The dish was weighed every 24h and measured continuously for 7 days. The water vapor transmission rate calculation formula is as follows:

wherein, Δ w is the weight change of the drying dish within the time t and the unit is g; tf is the thickness of the film in mm; a is the effective area of the film, in m 2; t is a time interval in units of d; Δ P is the water vapor pressure differential across the film, kPa; the saturated vapor pressures of pure water and saturated sodium chloride solution at 25 ℃ were 3.167kPa and 2.375kPa, respectively. All measurements were performed at least 3 times.

DPPH radical scavenging activity: weighing 1g of film sample, shearing, placing into a 10mL centrifuge tube, adding 5mL of absolute ethyl alcohol, shaking at 150rpm and 25 ℃ for 3h, and then centrifuging at 4000rpm for 10 min. Adding 1mL of supernatant into 4mL of ethanol solution (0.2mmol/L) of LDPPH, vortexing, mixing thoroughly, and storing in dark place for 30 min. The absorbance of the mixture was measured at 517 nm.

In the formula: a. the ₀ Is a light absorption value measured after mixing a DPPH free radical scavenger and ethanol; a. the ₁ Is the light absorption value measured after the DPPH free radical scavenger is mixed with the sample; a. the ₂ Is the absorbance value measured after the sample is mixed with ethanol.

And (3) antibacterial property measurement: food-borne pathogenic bacteria escherichia coli (cmcc) (b)44102 and staphylococcus aureus (staphylococcus aureus) cmcc (b)26003 were used to measure the antimicrobial activity of the membranes. The bacteria were cultured in Miller Hayton Broth (Mueller-Hinton Broth, MHB) at 37 ℃ for 24h and then further diluted with sterile sodium chloride solution (0.85%, w/v) to give a Broth containing a concentration of about 106 CFU/mL. Then, 1mL of the above-mentioned bacterial suspension was added to 9mLMHB so that the final bacterial suspension concentration was 105 CFU/mL. The composite film (2 cm. times.2 cm) was sterilized under ultraviolet rays for 1 hour, immersed in the broth and cultured at 37 ℃ for 24 hours. To evaluate the antibacterial activity of the samples, the growth of the bacteria was observed by plate counting.

The parameters of comparative example 1, comparative example 2, comparative example 3, example 1 and experimental example 2 were tested according to the above-described methods and are shown in fig. 10 and fig. 11.

The results show that the addition of oregano oil increases the thickness, tensile strength, elongation at break, antioxidant properties and antimicrobial properties of the film and reduces the water content, water solubility and water vapor transmission rate of the film. The nano phytoglycogen enhances the water solubility, tensile strength and elongation at break of the film, and reduces the water content and water vapor transmission rate of the film. Compared with single addition, the nano phytoglycogen and the oregano oil can be added in a mixing manner to reduce the swelling degree and the water vapor transmission rate of the film and enhance the tensile strength, the elongation at break and the antibacterial property of the film. As can be seen, the OEO/PG/SA composite membrane (1:1:10) has the best membrane forming performance.

The films prepared in the examples 1-3 and the comparative examples 1-2 are compared with the existing preservative film commodities, applied to apple preservation, and tested for the preservation effect, and the specific steps are as follows:

and (3) testing the preservation effect:

selecting undamaged red Fuji apples with similar sizes and ripeness, peeling, cleaning, airing, cutting into blocky fruits with similar sizes, and respectively processing the fresh-cut red Fuji apples by the following methods, wherein the apples are specifically divided into the following six groups: (1) the fresh-cut apples were designated as CK1 without any treatment; fresh-cut apples were wrapped with the SA film obtained in comparative example 1, designated CK 1; (2) the OEO/SA composite membrane (1:10) obtained in the comparative example 2 is used for wrapping fresh-cut apples and is named as CK 2; (3) wrapping fresh-cut apples with a commercially available PE preservative film, and naming the apple as CK 3; (4) the OEO/PG/SA composite membrane (1:1:10) obtained in example 1 is used for wrapping fresh-cut apples and is named as T-1; (5) the OEO/PG/SA composite membrane (5:1:10) obtained in the example 2 is used for wrapping the fresh-cut apples and is named as T-2; (6) the OEO/PG/SA composite film (2:1:10) obtained in example 3 was used to wrap fresh-cut apples and named T-3.

All the treatment groups are put into a breathable PE packaging box and stored in a refrigerator at 4 ℃. Taking 10.0g of pulp tissue on

days

0, 1, 2, 3 and 4 respectively, freezing with liquid nitrogen, and storing in a refrigerator at-80 deg.C.

The influence of the OEO/PG/SA composite membrane on the quality of fresh-cut apples during storage is explored by taking the weight loss rate, the color difference, the hardness, the content of soluble solids, titratable acid, ascorbic acid, the total number of colonies and the like as indexes, so that the application value of the composite membrane in practice is evaluated.

And (3) weight loss rate measurement: the mass loss of the fresh-cut fruits during storage was measured by weighing, three times per treatment, and the average value was taken. The weight loss (%) is calculated as follows:

wherein W is the mass loss rate of the nth day after treatment and the unit is percent; w ₀ Is the initial mass in g; w is a group of ₁ The mass measured after the n day of treatment is given in g.

Conclusion analysis: the results are shown in fig. 3, in which the weight loss rate of the fruits in each treatment group during storage showed an upward trend and the change was significant. The weight loss rate of the treatment group of the surface covering composite membrane is obviously lower than CK 1. Of these, CK3 was most effective in reducing the weight loss rate, followed by the T-1, T-2 and T-3 treatment groups.

And (3) measuring color difference: and measuring the color change condition of the fresh-cut apples in the preservation process by using a CR-400 handheld color difference meter. Two central points are selected on two cross sections of the apple respectively, two central points are selected on the outer surface for measurement, the six measured points are averaged, three points are processed in parallel each time, and the L value of the apple is measured. The larger the value of L, the brighter the surface color of the fresh-cut apple, the smaller the browning degree, and the abscissa is days.

Conclusion analysis: the change in whiteness of the surface pulp during storage of freshly cut "red fuji" apples is shown in fig. 4, with the L value of the fruit showing a decreasing trend during storage. Compared with CK1, the T-1 and T-2 treatment groups both have better color protection effect, and the T-3 treatment group only has poorer color protection effect.

And (3) hardness measurement: cutting the fruits into a sheet sample with the thickness of 1cm to be tested, selecting a plastic cylindrical probe with the diameter of 1cm, and randomly selecting 6 points to test the hardness.

Conclusion analysis: hardness is one of the important indicators of the quality of the picked apples, and the hardness is greatly reduced due to the action of cell wall degrading enzymes and dehydration in the storage process, so that the quality of the apples is reduced. As shown in FIG. 5, the hardness of the fresh-cut apples showed a decreasing trend as a whole, and compared with CK1, CK2 and CK3, the hardness of the T-1 and T-2 treated groups was significantly increased, indicating that the quality characteristics of the fresh-cut apples can be well maintained, the T-3 treated group can maintain higher hardness in the first three days, and the hardness value at day 4 is significantly decreased and is lower than CK 1.

And (3) measuring the content of total soluble solids: the content of Total Soluble Solid (TSS) in the fruit is measured by abbe refractometer method.

Conclusion analysis: the content of soluble solids, mainly including water-soluble sugars and acids, vitamins and minerals, is an important parameter for evaluating the quality of fruits during storage. As shown in FIG. 6, the T-1 treatment group maintained a slow-rising trend, while the T-2 and T-3 treatment groups both decreased and increased rapidly, indicating that they both had a better fresh-keeping effect. The dehydration process of the fruit and the solubilization of cell wall polyglycosides and hemicellulose during ripening can result in an increase in the soluble solids content. Thus, the soluble solids content increases during apple ripening, which in turn reduces the soluble solids content due to respiration. It can be seen that since polyethylene in the PE film can further ripen apples, the level of soluble solids of CK3 continues to decrease due to enhanced respiration. However, the content of soluble solids in the T-1 treated group increased slowly with the passage of time, so that it was found that the apple covered with the film had a slow ripening process, a low respiration rate and an excellent storage effect.

Titratable acid determination: weighing 10g of sample, adding 50mL of deionized water, crushing in a juice extractor, folding gauze in half for three times, and filtering. And (3) diluting the filtrate to 100mL, putting 20mL into a 100mL conical flask, adding 3-4 drops of phenolphthalein indicator, and titrating to reddish color within 1min by using 0.1mol/LNaOH calibrated by potassium hydrogen phthalate. The volume (V) of sodium hydroxide solution consumed was recorded. Each sample was assayed in triplicate and the average was taken. The titratable acid calculation is as follows:

in the formula: v is the volume of the sodium hydroxide standard solution consumed, and the unit is mL; c is the concentration of the sodium hydroxide standard titration solution, and the unit is mol/L; w is the sample mass in g; k is the conversion factor for the main acid, i.e. 1mmol of sodium hydroxide corresponds to the grams of the main acid. Here malic acid, so the K value was 0.067.

Conclusion analysis: the main component of titratable acid is organic acid, and the proportion of the organic acid to soluble solid directly influences the mouthfeel of fresh-cut apples. Also, titratable acids are substrates for enzymatic reactions during respiration. As shown in FIG. 7, as the storage time increased, the titratable acid content of the fresh-cut apples all showed a tendency of increasing and then decreasing, and only the T-1 treatment group continued to increase. Higher titratable acid content (lower pH value) indirectly indicates that the metabolism of organic acid is reduced, the respiration process of fruits and vegetables is delayed, and the quality of fresh-cut apples can be effectively maintained. Therefore, T-1, T-2, T-3 and CK3 all have excellent fresh-keeping effect.

Ascorbic acid assay: refer to the third method 2, 6-dichloroindophenol titration method in GB 5009.86-2016 (determination of ascorbic acid in food) to determine the ascorbic acid content in fresh-cut apples. . 1mL of dye corresponds to 0.0521mg of ascorbic acid. The ascorbic acid calculation formula is as follows:

in the formula: v ₁ The average number of milliliters of dye consumed to titrate a sample; v ₂ Average milliliters of dye consumed for titration of the blank; v is the total volume of the sample extracting solution; v ₃ The number of milliliters of sample extract taken at the time of titration; m is the amount (mg) of ascorbic acid that the lmL dye can oxidize; w is the weight (g) of the sample to be tested.

Conclusion analysis: the ascorbic acid has strong reducibility and is an important nutrient and an antioxidant component of the apples. The apple has high content of ascorbic acid, can keep fresh color, and has low content of ascorbic acid, which deepens brown color and affects quality of apple. As shown in FIG. 8, the ascorbic acid content of the "Red Fuji" fresh-cut apples generally decreased during storage. The content of the ascorbic acid in the fresh-cut apples of the T-1 and T-2 treatment groups is obviously higher than that of the fresh-cut apples of other groups, and the fresh-keeping effect is better. The T-3 treatment group composite film has poor fresh-keeping effect and cannot well maintain the content of the ascorbic acid.

Determination of antibacterial Properties: the total number of the colonies is determined by referring to GB 4789.2-2016 (national food safety Standard food microbiology test total number of colonies determination). Three replicates of each gradient were averaged to obtain the total number of colonies.

Conclusion analysis: the proliferation of microorganisms can make the fresh-cut apples inedible, so the colony count of bacteria is the most important index influencing the quality of the apples. As shown in FIG. 9, the T-1, T-2 and T-3 treated composite membranes have excellent bacteriostatic performance, and the total number of colonies is significantly lower than CK1, CK2 and CK 3.

In conclusion, compared with CK1, CK2 and CK3, the T-1, T-2 and T-3 treated composite membrane can effectively maintain the quality characteristics of fresh-cut apples, better maintain the color and hardness of the fresh-cut apples, effectively reduce water loss, keep higher soluble solid content, titratable acid and ascorbic acid content and inhibit the growth and propagation of bacteria.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also included in the scope of the present invention.

Claims

1. An edible nano composite film is characterized by comprising the following components in parts by weight: 0.1-0.2 part of hydrophilic nano phytoglycogen, 0.1-0.2 part of oregano essential oil, 1-2 parts of sodium alginate, 1-2 parts of tween 80, 1-2 parts of glycerol and 0.01-0.02 part of calcium chloride.

2. The edible nanocomposite film according to claim 1, comprising the following components in parts by weight: 0.1 part of hydrophilic nano phytoglycogen, 0.1 part of oregano essential oil, 1 part of sodium alginate, 1 part of tween 80, 1 part of glycerol and 0.01 part of calcium chloride.

3. A method of preparing the edible nanocomposite film according to any one of claims 1 to 2, comprising the steps of:

s1, dispersing sodium alginate, glycerol and Tween 80 into a hydrophilic nano phytoglycogen aqueous solution, and dropwise adding oregano essential oil under the condition of heating and stirring to obtain a mixed solution;

4. The method of claim 3, wherein the heating and stirring temperature is 60-70 ℃ and the stirring speed is 80-100rpm in steps S1 and S2.

5. The method of claim 3, further comprising removing impurities from the aqueous solution of hydrophilic nano phytoglycogen by suction filtration.

6. A method of preparing the edible nanocomposite film according to claim 3, wherein the hydrophilic nano phytoglycogen is prepared by a method comprising the steps of:

7. A process for preparing the edible nanocomposite film according to claim 6, wherein in step K2, the pH is from 4.5 to 4.9.

8. A method of preparing the edible nanocomposite film according to claim 3, wherein the method of preparing the oregano essential oil comprises the steps of: and (3) soaking the dried oregano in absolute ethyl alcohol at room temperature, carrying out suction filtration, and carrying out rotary evaporation drying on an extracting solution obtained by suction filtration under a vacuum condition to obtain the oregano essential oil.

9. Use of the edible nanocomposite film according to claims 1-2 as a preservative film for preserving fruits and vegetables.

10. The use of claim 9, wherein the fruit or vegetable is fresh-cut fruit or vegetable.